Heat engine

ABSTRACT

A thermodynamic engine of the external-combustion type, including a motor unit with a driving cylinder and a pair of combustion chambers communicating with that cylinder during alternate downstrokes of its driving piston, further comprises an air compressor having a reciprocating piston synchronised with the driving piston to supply fresh compressed air to the chambers during alternate upstrokes preparatorily to injection of a fresh fuel charge and ignition of the resulting fuel-air mixture in one or the other chamber. After the end of every downstroke, during which the burning mixture from one of the combustion chambers enters the driving cylinder to exert a thrust upon its piston, communication between that chamber and the cylinder is maintained for a fraction of the immediately following upstroke whereby the fresh air now introduced into the chamber by the compressor also enters the driving cylinder to help purge it of combustion residues. The driving and compressor cylinders are coaxially disposed, as are the associated pistons which are concentric portions of a unitary body separated by an annular recess accommodating the inner or driving cylinder; the cylinders terminate in a head provided in a common transverse plane with a set of ports leading to the associated combustion chambers, the ports being controlled by respective valves actuated by a cam carrier which rotates about the cylinder axis.

United States Patent. [191 Milisavljevic HEAT ENGINE [76] Inventor: Milorad Milisavlievic, 181

Promenade des Anglais 06-Nice, Nice, France [22 Filed: Sept. 7,1972

21 Appl. No.: 287,091

[30] Foreign Application Priority Data Sept. 8, 1971 Switzerland 13155/71 521 US. Cl. 60/39.62 [51] Int. Cl. F02g 3/02 [58] Field of Search 60/39.62

[56] References Cited UNITED STATES PATENTS 970,063 9/1910 Lake (SO/39.62 X 1,849,347 3/1932 Dale 60/39.62 X

2,182,430 12/1939 Gersman 60/39.62 3/1942 Hanson I 60/39.62

, Primary Examiner-Clarence R. Gordon Attorney, Agent, or FirmKar1 F. Ross; Herbert Dubno [57] ABSTRACT A thermodynamic engine of the external-combustion July 30, 1974 type, including a motor unit with a driving cylinder and a pair of combustion chambers communicating with that cylinder during alternate downstrokes of its driving piston, further comprises an air compressor having-a reciprocating piston synchronised with the driving piston to supply fresh compressed air to the chambers during alternate upstrokes preparatorily to injection of a fresh fuel charge and ignition of the resulting fuel-air mixture in one or the other chamber.

After the end of every downstroke, during which the,

burning mixture from one of the combustion chambers enters the driving cylinder to exert a thrust upon its piston, communication between that chamber and the cylinder is maintained for a fraction of the immediately following upstroke whereby the fresh air now introduced into the chamber by the compressor also enters the driving cylinder to help purge it of combustion residues. The driving and compressor cylinders are coaxiallydisposed, as are the associated pistons which areconcentric portions of a unitary body separated by an annular recess accommodating the inner or driving'cylinder; the cylinders terminate in a head provided in acommon transverse plane with a set of ports leading to the associated combustion chambers,

the'ports being controlled by respective valves actuated by a cam carrier which rotates about the cylinder axis."

10 Claims, 6 Drawing Figures Pmmwm w 3.826.086

SHEU 3 OF 4 FIG. 5

PAIENIED IR 3.826.086

sum u 0F 4 FIG. 6

an equal rotational speed of the drive shaft, twice the number of driving explosions per unit time can be produced with the first-mentioned engines than with the others but with a lesser. thermal efiiciency. This lesseningof the thermal efficiency essentially depends on the little time available to atwo-stroke engine for the intake of fuel, for achieving the combustion of the resultant mixture and for exhausting the burnt gases.

The present invention proposes providing a reciprocating heat engine having the advantages of a conventional two-stroke engine while obviating the drawbacks thereof due to the limited amount of time available for the combustion of the combustible mixture and in which may be used liquid or gaseous fuels which have a low calorific value or which are difficult to ignite, whilst ensuring integral combustion thereof. The heat engine provided by the invention comprises a source of compressed air, a piston and cylinder arrangement, a connecting rod and crank assembly connecting the piston to a rotary shaft, first and second combustion chambers, first and second pairs of valves respectively associated with said first and second combustion chambers with the first valve of each pair disposed between its associated chamber and the air source and with the second valve of each pair disposed between its associated chamber and the cylinder, a device for injecting fuel into each chamber and a member for igniting said fuel, means for operating each injection device and each ignition member, a valve for connecting the cylinder to the outside atmosphere, and means for controlling said valves.

The invention also provides a method of putting this engine into action, which comprises, during a first stroke of. the piston in the cylinder, from its bottom dead point (BDP) to its top dead point (TDP), introducing a charge of compressed air into the first of said combustion chambers, letting a constant volume combustion, begun during the previous cycle, carry on in the second chamber and connecting the cylinder with the atmosphere, during a second stroke of the piston,

from its TDP to its BDP, injecting a charge of fuel into the first chamber, igniting the mixture of fuel and compressed air contained in thischamber so as to achieve a constant volume'combustion of this mixture, interrupting theconnection of the cylinder with the atmosphere, putting the second combustion chamber and the cylinder into communication so as to achieve variable volume combustion in the second chamber and in the cylinder and hence a driving thrust on the piston,

ture of fuel and compressed air contained in this chamher so as to achieve a constant volume combustion of the mixture.

In the accompanying'drawings:

FIG. 1 is a schematic block representation illustrating the principleof the engine according to the present invention;

FIG. 2 is an explanatory diagram of the operation of the FIG. 1 engine;

FIG. 3 illustrates, in section, along line III-Ill of FIG. 4, the main parts of one constructional form of embodiment'of the engine according to the invention;

FIG. 4 is a section along line IV-IV of FIG. 3;- FIG. 5 is an explanatory diagram of the operations of the engine shown in FIGS. 3 and 4; and

FIG. 6 illustrates, in section, a variant of the engine 1 shown in FIGS. 3 and 4.

The heat engine schematically illustrated in FIG. 1 comprises an air compressor Co, which may either be of the piston or rotary type, two constant volume combustion chambers C, and C,, connected to the compressor Co through a conduit t, and through a conduit t, respectively, and a piston and driving cylinder arrangement, M, connected to the chambers C and C, through conduits t and t, respectively.

The entry of compressed air, from the compressor Co, into the two combustion-chambers C, and C, can be interrupted by closing valves S, and S, respectively, arranged at the downstream endof the conduits t, and

t,, respectively. These valves are, for this purpose, sub-- jected to the action of cams K, and K, secured to shafts 11 and 12 respectively, which are driven off the shaft Ar of the driving cylinder arrangement M via a shaft l0 I controlled by the latter.

Although the chambers C, and C, have beenillustrated inthe form of rectangles, clearly they will have in actual fact a shape that is particularly adapted to thereof. In sucha case, the conduits t, and t, will clearly during a third stroke of the piston, again from its BDP to its TDP, letting the constant volume combustion begun during the preceding stroke carry on in the first chamber, introducing a charge of compressed air into the second chamber and connecting the cylinder with the atmosphere, and, during a fourth and final stroke of the piston, again from its TDP to its BDP, putting the of fuel into the second chamber and igniting the mixbe very short, e.g., a few centimeters.

The flow of gaseous fluid from one or other chamber C, and C, through the conduits t and t, respectively can be interrupted byclosingtwo valves S, and S arranged at the downstream end of the conduits t, and t, respectively. By way of modification, not shown, these valves could also be arranged at the upstream end of the said conduits.

The valves S and S, are subjected to the action of cams K and K, secured ,to shafts 13 and 14 respectively, these shafts also'being driven off the shaft Ar via the shaft 10. I

The chambers C, and C, each carry a fuel injection device, I, and I, respectively, and a member, A, and A,

respectively, for igniting this fuel, the injection device and the ignition member attributed to each chamber being actuated by an individual cam, K, and K,

respectively, mounted on'a shaft, '16 and 17 respec-- 'tively, driven by the shaft 10. The injectors I, and I,

ing the burnt gases, which can be closed off or be made to communicate with an exhaust conduit t, by a valve 8,. The valve S, is subjected to the action of a cam K,

mounted on a shaft 15 driven off the shaft 10.

In a variant, not shown, it would be possible, to mount the various cams K, to K, on a single cam shaft, controlled by the drive shaft Ar.

It should further be noted that, when the compressor Co is a piston compressor, the latter can be driven directly by the driving cylinder arrangement M, these two machines then having to be so coupled that'the piston of each moves simultaneously from its top dead point (TDP) to its bottom dead point (BDP) and vice versa.

Let us now see how the described heat engine is made to operate and for this let us refer to the diagram shown in FIG. 2.

The fact that the described heat engine comprises two combustion chambers implies that this engine operates according to a four-stroke combustion cycle for each chamber, these strokes being identified bythe Roman numerals I to IV. v

The diagram shows, as a function of these strokes, for how long and when the various valves S, to S, open (homonymous lines of the diagram), for how long and when fuel is injected into each chamber C, and-C, (lines I, and I,)and the instant when the combustible mixture in each'chamber is ignited (lines A, and A,).

The FIG. 2 diagram shows moreover when combustion in each of the combustion chambers C, and C, (lines C, and C,) in the engine cylinder takes place (line C For an engine having piston compressor, it shows also what are the compression strokes of the latter (strokes I and III of line Co).

At the beginning of stroke I of the cycle, the-valves S,, S, and S, are open and the valves S, and S, are closed. The piston of the driving cylinder arrangement M and that of the compressor Co are at their bottom dead point (BDP). As soon as the piston of the driving cylinder arrangement Mand that of'the compressor Co begin to move towards their top dead point (TDP), the first force's out the burnt gases, resulting'from a previous combustion, through the conduit and the second pumps air into the chamber C,. Since the valve 8, is open, this air escapes into the driving cylinder arrangement M and thus scavenges this chamber, and, admittedly partially, the cylinder. The valve S, rapidly closes (see line S, of the FIG. 2 diagram) and the piston of the driving cylinder arrangement M completes exhaustion towards the atmosphere of the combustion gases contained in the latter whereas the compressor Co supplies compressed air to the chamber C,. Throughout this first stroke, the chamber C, is closed and in it there takes place a constant volume combustion which began during the preceding cycle.

At the end of the first stroke, respectively at the beginning of stroke II, the valves 8, and S, are made to close and the valve S, is made to open. In addition, the cam K controls the injector 1,, so that the chamber C, receives a charge of fuel. There is thus formed in the chamber C, a fuel and compressed air mixture which will be all the more homogeneous if the fuel has been divided into small droplets, or even vaporized if it is sufficiently volatile. This mixture is ignited by the member A, as soon as the injection of fuel into the chamber ceases (line A, in the diagram). Since the chamber C, is cut off from the driving cylinder arrangement M, the combustion that results from this ignition takes place at constant volume and will also remain so throughout the next stroke (stroke III). Since, moreover, the valve S, is open, the combustion that takes place in the chamber C,,- and which previously was taking place at constant volume, can continue at variable volume inside this chamber and inside the driving cylinder arrangement M' whilst forcing back the piston thereof toits BDP. Stroke II is therefore a working stroke of the heat engine. During this same stroke, the compressor Co sucks in fresh air.

At the beginning of the third stroke, the valves 8,, S, and S, are open and the valves S, and S, are closed. In thechamber C,, which is completely isolated, the combustion which started during the previous stroke carries on at constant volume (see line C,). The chamber C, is,'however, connected to ,the compressor Co, which supplies it with fresh air under pressure as soon as the piston of the latter moves from its BDP to its TDP, this movement also being made by the piston of the driving cylinder arrangement M. The chamber C, is also connected, via the valve S4, to the cylinder of the arrangement M, thus enabling the fresh air from the compressor to scavenge the chamber C, and, partially, the cylinder of the arrangement M. Once the valve 8., has been closed, the compressor Co can fill the chamber C, with compressed airuntil the end of the third stroke, during which stroke the piston of the driving cylinder arrangement M attends to the discharge of the burnt gases filling the cylinder thereof.

- it takes place at constant volume for the remainder of v At the beginning of the next stroke (stroke IV), the valve S, is made to open whereas the other valves remain closed. Consequently, the combustion which was taking place in the chamber C, at constant volume during the major part of the second stroke and throughout the third stroke, can carry on at variable volume in this chamber C, and in the driving cylinder arrangement M.

The piston of the latter is pushed from the TD? to the BDP by the gases under pressure which invade it and this is the second driving stroke of the cycle.

At the beginning of the fourth stroke the chamber C, receives a charge of fuel via the injector I, so as to form in this chamber a combustible mixture which is subsequently ignited by supplying the member A, with electric current. The combustion begins in this chamber C,;

the combustion time, in a given working cycle, can be increased to 2n-l where n is the number of constant volume combustion chambers associated with one driving cylinder arrangement, each chamber forming with the cylinder arrangement one working unit having a working cycle of 2n;

the number of driving strokes'per working cycle of one cylinder-chamber unit can be increased to n;

' which normally cannot be used in internal combustion engines.

. In the described engine, the means used for preparing and burning the air-fuel mixture include the compressedair source Co, the two constant volume combustion chambers C and'C- the conduits t and t the valves S and 8,, the control means l0, 11, 12, K and K, for these valves, the fuel injection devices I and I the ignition members A and A, and their control means 16,, 17,10, and K Themeans for transmitting the energy of the gases to the drive shaft include the driving cylinder arrangement M with its connecting rod, the crank, the shaftAr, the valvess S and 8,, the means 13,14, 15, K K and K, controlling these valves, and the conduits t t and t With the engine comprising two constant volume combustion chambers per driving cylinder arrangement, the working cycle of each working unit consist-' ing of one chamber and of the driving cylinder arrangement thus comprises four strokes asis apparent from the description of the operation with reference to FIG. 2. Combustion takes place during three of the strokes: two constant volume strokes (during the second and third strokes in the case of chamber C and during the fourth and first strokes in thecase of chamber C and one variable volume stroke (during the fourth stroke in the case of chamber C, and during the second stroke in the case of chamber C The cycle comprisestwo driving strokes, one for each working unit (the fourth in the case of the working unit that includes chamber C,, and the second in the case of the working unit that includes the chamber C ln-the engine'illustrated in FIGS. 3 and 4 the compressed air source is formed by a compressor consisting of a piston and cylinder'arrangement operating in synchronism with the driving cylinder arrangement. The characteristic feature of this engine lies in the association of the compression cylinder arrangement with the driving cylinder arrangement so as to provide a power unit of minimal size with which maximum power output can be achieved for a given driving cylinder capacity,

compression ratio and rotational speed of the drive shaft.

The engine of FIGS. 3 and 4 comprises a cylinder 1 inside which is coaxially mounted a second cylinder 2 in the form of a sleeve which is secured by its flared upper end portion 2a to a head 3, the latter being in turn secured to a flared upperend portion 1a of the cylinder 1. In the cylinder 1 is slidably mounted a piston 4 having rings 4a and a circular slot 5 extending from its top end to a depth slightly greater than the length of the cylinder 2 which can thus slide in this slot 5 during axial movement of the piston 4 in the cylinder. The central portion of the piston 4 thus forms a piston 6 for the cylinder 2, which piston is also provided with rings 6a. The pistons 4 and 6-thus constitute, through their lower portions, a single part to which is'conv'entionally secured a rod 7 which connects the unit consisting of the two pistons 4 and 6 to a drive shaft not shown.

As will be observed, the piston 4 of cylinder 1 is an annular piston which slides between the inner surface of the cylinder 1 and the outer surface of the cylinder 2. Tolighten the pistons 4 and 6, these are hollowed out at 8 and 9 respectively. I

In the head are provided two combustion chambers 10 and 11 and two pairs of valves l2, l3 and 14, 15, the pair 12, 13 being associated with chamber 10 and the pair 14, 15 being associated with chamber 11, each pair respectively connecting the associated chamber to the cylinders l and 2. The valves are acted upon by springs 16, 17, 18 and 19 which tend to maintain the associated valves in the illustrated closed position. The stems of the valves 12 to 14 are each formed at their ends with notches 20, 21, 22 and'23 respectively cooperating with cams 24, 25, 26 and 27 that are secured to the untively. I In the lower end portion of the stem of valve 12 there is formed a passage 36 which causes the cylinder 1 to communicate, in any position of the valve, with a passage 37 formed in the head 3 along chambers 10 and 11. In the lower end portions ofthe stems of valves 13 to 15 are formed passages 38, 39 and 40 respectively which connect the passage 37 with another passage 41 formed in the head above the latter and in substantially parallel relationship therewith. The passages 36 to 41 thus together form a duct through which fresh air may be circulated to cool the valves and the combustion chambers as will be explained further on.

Along its inner surface, which slides on the outer surface of the cylinder 2, the piston 4 is formed with a groove 42 whose function will be explained hereafter.

As will be observed from FIG. 4, the engine comprises a further pair of valves 43 and 44, the first, 43,

for regulatingthe, intake of fresh air into the cylinder 1 via piping 45, and the second, 44, for regulating theexhaust of spent gases from the cylinder 2 via piping 46. The stems of the valves 43 and 44 are also provided with notches, not shown, which cooperate with cams, not shown, secured to the underside of the'wheel 28.

The described engine operates as follows:

Let us suppose that the valves 12 to 15 and the pistons 4 and 6 occupy the positions illustrated in FIG. 3, that the valves 43 and 44 are also closed, that the chamber 10 has just been filled with compressed air, in the course of the preceding stroke, and that in the chamber 11 constant volume combustion is taking place of the air and fuel mixture introduced and ignited during preceding strokes.

At the beginning of the next stroke, which we shall call the first stroke of the working cycle and which corresponds to a movement of the pistons 4 and 6 from their top dead point (TDP) to their bottom dead point (BDP), the valves 43 and are opened, fuel is injected into the chamber 10 by the device 32 and the resulting mixture is ignited by the plug 33 (see FIG. 5) to initiate constant volume combustion of this mixture. There further occurs, firstly, an expansion of the burning mixture in the chamber 11 from the latter into the driving cylinder 2, which mixture, whilst from then on being subjected to a variable volume combustion, re-

pels the driving piston 6 and hence the compression piston 4 to their BDP, and, secondly, an intake, into the compression cylinder 1, of fresh air and of the air contained in the cooling system 36-41, which entered the latter during the preceding compression stroke as will be explained below. At the end of this first stroke the valve 43 is closed.

-At the beginning of the next stroke, which we shall call the second stroke of the working cycle and which corresponds to the displacement of the pistons 4 and 6 from their BDP to their TDP, the valves 14 and 44 are opened, thus causing the air contained in the compression cylinder 1 to be compressed in the chamber 11 and the burnt gases contained in the driving cylinder 2 to be exhausted. Through the passage 36, formed in the valve 12, fresh air is also compressed in the duct 36 to 41 that providesthe cooling system for the valves and for the combustion chambers. Shortly after the beginning of this second stroke, the valve 15 (FIG. 5), which remained open at the end of the preceding stroke to enable the chamber 11 to be scavenged by the entering compressed air, is closed. At the end of this second stroke, the valves 14 and 44 are closed.

At the beginning of the next stroke, which we shall call the third stroke of the working cycle andwhich corresponds to a displacement of the pistons 4 and 6 from their TDP to their BDP, the valves 13 and 43 are opened, fuel is injected into the chamber 11 by the device 34 and the resulting mixture is ignited by the plug 35 to initiate a constant volume combustion of this mixture. There further occurs, firstly, expansion of the burning-mixture in the chamber 10 from the latter into the driving cylinder 2, which, whilst being subjected from then on to variable volume combustion, repels the piston 6 and hence the piston 4 towards their BDP, and,

secondly, an intake, into the cylinder 1, of fresh air and r from their BDP to their TDP, the valves 12 and 44 are opened, thus causing the fresh air contained in the compression cylinder 1, in the chamber 10 and inthe cooling system 36-41 to be compressed, and causing the burnt gases in the driving cylinder 2 to be exhausted. Shortly after the beginning of this fourth stroke, the valve 13 which remained open at the end of the third stroke is closed to enable the chamber 10 to be scavenged by the fresh air entering it. At the end of this fourth stroke, the valves 12 and 44 are closed.

' When the pistons 4 and 6 move from theirTDP to their BDP during the first and third strokes, the fresh air entering the cylinder 1 passes through the groove 42 in piston 4, surges into the slot 5 as the latter is being freed from the cylinder 2, and, .upon coming into contact with the surface of the piston, causes the latter to cool. During the second and fourth strokes, the air contained in the slot 5 is exhausted therefrom through the groove. 42 and is compressed in the combustion chambers and the cooling system. The piston 6 and the cylinder 2 are also cooled by the fresh air entering the slot 5 and escaping therefrom through the space between the inner'surface of the piston 4 and the outer surface of the cylinder 2.

In the described engine, the means used for preparing and burning the air and fuel mixture include a piston compressorconsisting of the cylinder 1 and of the piston 4, the connecting rod 7, the two constant volume combustion chambers 10 and 11, the valves 12, 14 and 43, the control means 16, 19, 20, 23, 24, 27, 28-31 for these valves, the fuel injection devices 32 and 34 and ignition members 33 and 35. The means for transmitting the energy of the gases to the drive shaft include a driving cylinder arrangement consisting of the cylinder 2 and of the piston 6, the connecting rod -7, the valves 13, 15 and 44 and the control means 17, 18, 21, 22, 25, 26 and 28-31 for these valves.

With the engine comprising two constant volume combustion chambers per driving cylinder arrangement, the working cycle of each unit consisting of one chamber and of the driving cylinder arrangement thus has four working strokes as is apparent from the above description of the operation (see FIG. 5). The combustion takes place during three strokes: two constant volume strokes (during the first and the second in the case of chamber 10 and during the third and fourth in the case of chamber 11) and one variable volume stroke (during the third in the'case of chamber 10 and during the first in the case of chamber 11). The cycle includes two driving strokes, one for each working unit (the first in the case of the unit that includes chamber 11 and the third in the case of the unit that includes chamber 10).

Theconstructional embodiment of the engine illustratedin FIGS. 3 and 4 thus has all the characteristic features and hence all the advantages of the engine schematically illustrated in FIG. 1. In addition it has the advantages attributableto its own particular design, the main one being the reduced number of parts needed to operate a compressor and a driving cylinderarrangement and hence the reduction to 'a minimum of the overall size of an engine of given power. Moreover,

with the described engine, the amount of air and fuel mixture and its compression ratio can, in the case of a particular driving'cylinder arrangement be varied by varying the capacity of the compression cylinder 1. The powerof the engine may also be increased without increasing the compression ratio by selecting a suitable ratio for the diameters of the pistons (cylinders).

The characteristic feature of the engine given by way of example, thus essentially consists in the manner in which is designed the assembly that includes the compressor and the driving cylinder arrangement, which design enables the useof a single cylinder unit, a single piston, a single connecting rod and a single crank, and further enables the actual manufacture of the engine to be simplified. I

It should be noted that this constructional principle may be applied to any other engine besides that described by way of example and which includes a piston and driving cylinder arrangement, at least one combustion chamber connected by valves firstly tothis driving cylinder arrangement and secondly to a compressedair source.

The variant shown in FIG. 6 .differs from the constructional embodiment shown in FIG. 3 in that a third 'chamber 47 is disposed between the chambers l-and 11 and the driving cylinder 2 and is connected to the latter by a valve 48. A passage 49 is formed inside the stem of the valve 48 to enable the passages 37 and 41 to communicate. The valve 48 is provided with a return spring 5 0 and, at the end of its stem, with a notch 51 cooperating with a cam 52 secured to the topside of the .and 11 on to the top face of the piston 6. The actuation of the valve 48 issynchronized' with that of the valves 13 and 15, i.e.', it is opened at the beginning of the first and third strokes and closed shortly after'the beginning of the second and fourth strokes.

The chamber 47 may be filled either with compressed fresh airor with air and fuel mixture. In this case, the valves 13 and 15 connecting the combustion chambers 10 and 11 to the chamber 47 will be closed at the beginning of the third and first strokes, respectively, a little after the valve 48, to enable the compressed air to enter the chamber 47. This air will assist the combustion of the gases issuing from the chambers 10 and 11. Fuel may also be injected into the compressed air in the chamber 47; in this case the air and fuel mixture will ignite spontaneously upon coming into contact with the gases issuing from the chambers 10 and 11, thereby causing an explosion and hence an increase in the action of the gases on the piston 6.

Further modifications maybe made to the described engines without departing from the spirit and scope of the invention. Thus, for instance, the valve control means given by way of example may be replaced by other suitable means. The same applies to the system for cooling the valves, the chambers and the driving cylinder arrangement.

I claim:

1. A thermodynamic engine comprising:

a motor unit with a driving cylinder and a driving piston. reciprocable therein; I

a drive shaft linked with said driving piston for rotation thereby; Y

a firstand a second combustion chamber;

' a source of compressed air including a compressor cylinder and a compressor piston reciprocable therein, said pistons being interconnected for synchronous reciprocation;

first valve means for connecting said compressor cylinder with said first chamber during a first stroke of said pistons in a four-stroke working cycle;

second valve means for connecting said compressorcylinder'with said second chamber during a third fifth valve means for venting said cylinder to the atmosphere during said first and third strokes;

first injection means for charging said first chamber with fuel after said first stroke and before said fourth stroke;

first ignition means for igniting the air-fuel mixture in said first chamber after operation of said first injection means and before said fourth stroke, thereby initiating a combustion at constant volume in said first chamber prior to operation of said third valve means with subsequent transfer of combustion to said driving cylinder during said fourth stroke;

second injection means for charging said second chamber with fuel after said third stroke and before the second strokeof the next cycle;

second ignition means for igniting the air-fuel mixture in said second chamber after operation of said second injection means and before said second stroke of the next cycle, thereby initiating a combustion at constant volume in said second chamber prior to operation of said fourth valve means with subsequent transfer of combustion to said driving cylinder during said second stroke of the next cycle; and

control means for said valves, said first and second injection means and said. first and second ignition means operatively coupled with said drive shaft.

2. A thermodynamic engine comprising:

an outer cylinder;

an inner cylinder coaxial with said outer cylinder defining therewith an annular space;

an annular outer piston reciprocable in said space;

an inner piston reciprocable in said inner cylinder, said pistons being rigidly interconnected at an axial location beyond said inner cylinder;

a drive shaft linked with said pistons atsaid location for rotation thereby;

a head common to both cylinders at an end thereof remote from said location, said head being provided with a. first combustion chamber, a second combustion chamber, a first port leading from said outer cylinder to said first chamber, a second port leading from said outer cylinder to said second chamber, a third port leading from said first chamber to said inner cylinder, a fourth port leading from said second chamber to said inner cylinder, a fresh-air inlet communicating with said outer cylinder, and an outlet communicating with said inner cylinder;

I a first, a second, a third, a fourth, a fifth and a sixth first injection means for charging said first chamber with fuel;

first ignition means for igniting an air-'fuel mixture in said first chamber;

second injection means for charging said second chamber with fuel; second ignition means for igniting an air-fuel mixture in said second chamber; and

control means for said valves, said first and second injection means and said first and second ignition means operatively coupled with said drive shaft for opening said inlet during a first and a third stroke of a four-stroke working cycle of said pistons, opening said outlet during a second and a fourth stroke of a cycle, opening said first port during said fourth stroke, opening said second port during said second stroke, opening said third port during said third stroke, opening said fourth port during said first stroke, successively actuating said first injection and ignition means in the first half of a cycle, and successively actuating said second injection and ignition means in a second half of a cycle.

3. An engine as defined in claim 2 wherein said control means is operative to keep said third port open during an initial fraction of said fourth stroke and to keep said fourth port open during an initial fraction of said second stroke.

4. An engine as defined in claim 3 wherein said control means is'operative to actuate said first injection and ignition means at the beginning of said first stroke and to actuate said second injection and ignition means at the beginning of said third stroke.

5. An engine as defined in claim 2 wherein said ports are disposed in a common plane transverse to the axis of said cylinders:

.6. An engine as defined in, claim 2 wherein said head is formed with a pair of manifolds, said first .valve having a stem provided with an internal passage open to said first port and to one of said manifolds, said second, third and fourth valves having stems provided with internal passages open to both said manifolds, whereby air from said outer cylinder can circulate through said passages for cooling said stems.

7. An engine as defined in claim 2 wherein said control means comprises a set of cams coacting with all said valves and a carrier for said cams rotatable about the axis of said cylinders. I

8. An engine as defined in claim 2 wherein said pistons are part of a unitary body provided with an annular recess centered on said axis, said recess separating said pistons from each other and accommodating said inner cylinder.

9. An engine as defined in claim 8 wherein said body is provided with an axially extending groove open to said recess and communicating with said outer cylinder for pumping fresh air into and out of said recess during reciprocations of said body.

' 10. An engine as defined in claim 2 wherein said head is provided with a central chamber communicating'via said third and fourth portswith said first and second chambers and via a fifth port with said inner cylinder, further comprising a fifth valve in said head actuatable by said control means to open said fifth port simultaneously with the opening of said third and fourth ports by said third and fourth valves. 

1. A thermodynamic engine comprising: a motor unit with a driving cylinder and a driving piston reciprocable therein; a drive shaft linked with said driving piston for rotation thereby; a first and a second combustion chamber; a source of compressed air including a compressor cylinder and a compressor piston reciprocable therein, said pistons being interconnected for synchronous reciprocation; first valve means for connecting said compressor cylinder with said first chamber during a first stroke of said pistons in a four-stroke working cycle; second valve means for connecting said compressor cylinder with said second chamber during a third stroke of a cycle; third valve means for connecting said first chamber with said cylinder in a fourth stroke of a cycle and during an adjoining fraction of the first stroke of the next cycle; fourth valve means for connecting said second chamber with said cylinder in a second stroke of a cycle and during an adjoining fraction of said third stroke; fifth valve means for venting said cylinder to the atmosphere during said first and third strokes; first injection means for charging said first chamber with fuel after said first stroke and before said fourth stroke; first ignition means for igniting the air-fuel mixture in said first chamber after operation of said first injection means and before said fourth stroke, thereby initiating a combustion at constant volume in said first chamber prior to operation of said third valve means with subsequent transfer of combustion to said driving cylinder during said fourth stroke; second injection means for charging said second chamber with fuel after said third stroke and before the second stroke of the next cycle; second ignition means for igniting the air-fuel mixture in said second chamber after operation of said second injection means and before said second stroke of the next cycle, thereby initiating a combustion at constant volume in said second chamber prior to operation of said fourth valve means with subsequent transfer of combustion to said driving cylinder during said second stroke of the next cycle; and control means for said valves, said first and second injection means and said first and second ignition means operatively coupled with said drive shaft.
 2. A thermodynamic engine comprising: an outer cylinder; an inner cylinder coaxial with said outer cylinder defining therewith an annular space; an annular outer piston reciprocable in said space; an inner piston reciprocable in said inner cylinder, said pistons being rigidly interconnected at an axial location beyond said inner cylinder; a drive shaft linked with said pistons at said location for rotation thereby; a head common to both cylinders at an end thereof remote from said location, said head being provided with a first combustion chamber, a second combustion chamber, a first port leading from said outer cylinder to said first chamber, a second port leading from said outer cylinder to said second chamber, a third port leading from said first chamber to said inner cylinder, a fourth port leading from said second chamber to said inner cylinder, a fresh-air inlet communicating with said outer cylinder, and an outlet communicating with said inner cylinder; a first, a second, a third, a fourth, a fifth and a sixth valve in said head for closing and opening said first port, said second port, said third port, said fourth port, said inlet and said outlet, respectively; first injection means for charging said first chamber with fuel; first ignition means for igniting an air-fuel mixture in said first chamber; second injection means for charging said second chamber with fuel; second ignition means for igniting an air-fuel mixture in said second chamber; and control means for said valves, said first and second injection means and said first and second ignition means operatively coupled with said drive shaft for opening said inlet during a first and a third stroke of a four-stroke working cycle of said pistons, opening said outlet during a second and a fourth stroke of a cycle, opening said first port during said fourth stroke, opening said second port during said second stroke, opening said third port during said third stroke, opening said fourth port during said first stroke, successively actuating said first injection and ignition means in the first half of a cycle, and successively actuating said second injection and ignition means in a second half of a cycle.
 3. An engine as defined in claim 2 wherein said control means is operative to keep said third port open during an initial fraction of said fourth stroke and to keep said fourth port open during an initial fraction of said second stroke.
 4. An engine as defined in claim 3 wherein said control means is operative to actuate said first injection and ignition means at the beginning of said first stroke and to actuate said second injection and ignition means at the beginning of said third stroke.
 5. An engine as defined in claim 2 wherein said ports are disposed in a common plane transverse to the axis of said cylinders.
 6. An engine as defined in claim 2 wherein said head is formed with a pair of manifolds, said first valve having a stem provided with an internal passage open to said first port and to one of said manifolds, said second, third and fourth valves having stems provided with internal passages open to both said manifolds, whereby air from said outer cylinder can circulate through said passages for cooling said stems.
 7. An engine as defined in claim 2 wherein said control means comprises a set of cams coacting with all said valves and a carrier for said cams rotatable about the axis of said cylinders.
 8. An engine as defined in claim 2 wherein said pistons are part of a unitary body provided with an annular recess centered on said axis, said recess separating said pistons from each other and accommodating said inner cylinder.
 9. An engine as defined in claim 8 wherein said body is provided with an axially extending groove open to said recess and communicating with said outer cylinder for pumping fresh air into and out of said recess during reciprocations of said body.
 10. An engine as defined in claim 2 wherein said head is provided with a central chamber communicating via said third and fourth ports with said first and second chambers and via a fifth port with said inner cylinder, further comprising a fifth valve in said head actuatable by said control means to open said fifth port simultaneously with the opening of said third and fourth ports by said third and fourth valves. 